The present invention generally relates to window coverings and, more particularly, relates to cordless blinds and shades.
A variety of window covering devices currently exist, including retractable shades and venetian blinds. In conventional venetian blinds, a plurality of slats are supported in ladder cords that extend between a head rail and a bottom rail. One or more take-up cords extend from the bottom rail, through the slats, and out of the head rail. Upward force on the take-up cords lifts the bottom rail towards the head rail, gathering the slats, from the lowermost to the uppermost.
In such blinds, the take-up cords are manually-operated. More specifically, the take-up cords which extend from the bottom rail, through the slats, and out of the head rail are drawn upon by a user which thereby lifts the bottom rail and hence the slats. A lock is typically provided to secure the take-up cord so that the blinds may be secured at various positions between a lowered, extended position, and a raised, fully retracted, position.
More recently, in cordless blind products, a spring motor has been provided that is coupled to a take-up drum to which the take-up cord is secured. The spring motor provides a lifting force to the take-up cord. Such spring motors provide smooth operation of the blind, and avoid lengthy cords extending from the blind which can be unsightly and become tangled thereby inhibiting operation of the blind.
With a cordless blind product, balancing of the spring motor force is difficult. As the blind is extended, the slats become supported by the ladder cords, and the weight supported by the spring motor reduces. Conversely, when the blind is retracted, the weight of the bottom rail and all the slats needs to be supported by the spring motor. Unless a spring motor provides a corresponding variable force, a number of problems may occur. For example, if the spring motor does not provide enough lifting force, the blind may not remain in the fully retracted position and may slowly fall downward. If the spring motor provides too much lifting force, the blind may not remain at an extended position, and the blind may slowly creep upward.
In practice, constant force spring motors sized to support the expected full weight of the slats may be used and an external mechanism, such as a clutch, may be used to lock the spring motor when the blind is at the desired location. However, such devices typically do not provide smooth operation.
Variable force spring motors have therefore been developed and permit the blind to be extended to virtually any position from fully retracted to fully extended. Still, sizing the spring motor is difficult. The variable force can be generated by using a spring member tapered in width, thickness and/or diameter which thus results in a force curve having its greatest force when the blind is retracted, and its lowest force when the blind is extended. Depending on the size and weight of the slats and bottom rail, the spring motor can be sized accordingly, or multiple spring motors may be used.
Even with such variables force spring motors, the introduction of friction to the system can be advantageous. Such additional friction creates a wider acceptable operational range for a given size of spring motor. However, if too much friction is added to the system, operation of the spring motor and blind will not be smooth. Moreover, it is desirable for the friction to be added only when the blind is being retracted and for little or no additional friction to be added when the blind is extended.
In accordance with one aspect of the invention, a window shade is provided which comprises an expandable covering, the covering being movable in a first direction when expanding to cover a window, the covering being movable in a second direction when retracting away from the window, a spring motor operably connected to the expandable covering to move the covering in the second direction, a rotating output connected to the spring motor, and a retarder associated with the rotating output, the retarder introducing resistance to movement of the covering in the second direction while not introducing resistance to movement of the covering in the first direction.
In accordance with other aspects of the invention, the retarder includes a one-way bearing or a brake.
In accordance with another aspect of the invention, a blind is provided which comprises an expandable covering, the covering being movable in a first direction when expanding, and in a second direction when retracting, a cord connected to the expandable covering, the cord being movable in a first direction when the covering is retracted and in a second direction when the covering is expanded, a spring motor connected to the cord for moving the covering between the retracted position and the expanded position, and a one-way roller in engagement with the cord for adding resistance to the movement of the cord in the first direction.
In accordance with another aspect of the invention, a blind is provided comprising an expandable covering, the covering being movable in a first direction when expanding and in a second direction when retracting, a cord connected to the expandable covering, a cord spool connected to the cord, a spring motor connected to the cord spool by a rotatable shaft, and a brake adapted to impart a first force against the shaft when the expandable covering moves in the first direction, and a second, higher, force when the expandable covering moves in the second direction.
In accordance with yet another aspect of the invention, a spring motor assembly is provide including a frame, a take-up drum pivotally mounted to the frame, a drive drum pivotally mounted to the frame, a coil spring interconnected between the take-up drum and the drive drum, a rotating member operatively connected to the drive drum, and a retarder associated with the rotating member. The retarder introduces resistance to the rotating member in a first direction of rotation and not in a second direction of rotation.
These and other aspects and features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.